No treatments are known for practically all types of hereditary retinitis pigmentosa. Thousands of patients including many young children become blind from these degenerations. New information about retinal abnormalities has been obtained through electrophysiological testing of asymptomatic or minimally symptomatic siblings of clearly affected individuals. The electroretinogram (ERG) and early receptor potential (ERP) abnormalities have shown that different types of photoreceptor malfunction exist in the different genetic types of retinitis pigmentosa. These recordings have made it possible to establish a diagnosis of retinal degeneration early in life even when ophthalmoscopic changes may be minimal and when retinal function is relatively preserved. Changes in ERG implicit times of rod and/or cone components have provided an important index of the widespread extent of these retinal degenerations even in the early stages. Extensive visual loss appears to be inevitable for the overwhelming majority of untreated patients with night blindness and abnormal cone and rod ERG implicit times. The specific aims of this project are as follows: to detect and define further with the ERG and ERP the receptor abnormalities in children who have older relatives affected with retinitis pigmentosa; to study the ERP waveform in patients with different types of retinal degenerations; to continue investigations on ERG implicit time; to develop further guidelines for estimating visual prognosis; to study the progressive retinal degenerations seen in patients who have other associated abnormalities. It is hoped that early diagnosis and research on the pathogenesis of these diseases will lead to treatments for these patients. Investigations are in progress to simulate and study in animals the electrophysiological abnormalities detected in affected patients. The effects of drugs, diet and light on the function and structure of the photoreceptors and pigment epithelium are under study.